Over the past century, the heads of Japanese people have evolved to become rounder, featuring narrower cheekbones, broader upper jaws, and noses that are finer and more prominent, according to Shiori Usui of the National Museum of Nature and Science in Tsukuba, Japan. While shifts elsewhere might differ, this general trend is likely mirrored globally, the study suggests. The findings of this new research have been documented in the American Journal of Biological Anthropology.
Usui notes that researchers frequently reference human skeletal remains from the 19th and early 20th centuries as a benchmark for what is considered “modern” humanity. However, it is a known fact that contemporary individuals are typically taller and larger than those from a hundred years ago, largely attributable to improvements in health, nutrition, and environmental factors. Usui and her associates hypothesized that these same influences could also be impacting cranial shape.
To explore this, the investigators performed computed tomography (CT) scans on the skulls of 34 males and 22 females who passed away from natural causes between 1900 and 1920. Their bodies had previously been donated to the Kyoto University Faculty of Medicine for dissection and subsequently became skeletal specimens housed in a museum.
The team also gathered scan data from 29 men and 27 women who died between 2022 and 2024. Their bodies underwent post-mortem imaging, an increasingly common practice in Japan that has resulted in a substantial “virtual skeleton collection,” as Usui describes it.
Researchers utilized 161 reference points on the 3D skull images to quantify shape, identifying minor yet relatively consistent alterations over time. Specifically, people have become more brachycephalic; their skulls have largely lost the elongated, oval conformation prevalent when heads were longer from front to back and narrower side-to-side in the early 20th century.
Although this aligns with hypotheses put forth by other scientists based on living populations, the CT analysis of deceased individuals revealed a host of other unexpected differences, Usui commented. Beyond the changes in cheekbone, nose, and upper jaw configuration, the forehead has become shorter—originating from a higher facial position—and slightly more concave over time, the team reports. Furthermore, the bony protrusions situated behind the ears, known as mastoid processes, have grown larger and more pronounced.
These modifications appear too recent to be the product of genetic evolution, Usui suggests. They are more likely outcomes of lifestyle influences, such as enhanced childhood health and nutrition, alongside the consumption of softer foods that require less strenuous chewing.
The team discovered that the distinctions between male and female skulls have widened compared to a century ago: male crania exhibit more pronounced brow ridges, larger mastoid processes, and faces that project further forward than those of females.
“This was a striking and unanticipated finding for us,” Usui stated, as her team had theorized that the convergence of male and female lifestyles would result in diminished physical divergence. “We anticipated observing more ‘neutralized’ facial features. Instead, our analysis demonstrated the opposite: sexual dimorphism has actually intensified.”
A 2024 study conducted in the United States indicated comparable trends of change in both male and female faces over time, she mentioned. Yet, a different, earlier US-based study from 2000 pointed toward an opposing shift in overall head shape—it had become more oval than round—over the preceding 100 years. This discrepancy might be attributable to technical limitations in the earlier research, along with the impact of ethnic shifts driven by substantial population immigration in the US.
“We are eager to see more global studies to understand how distinct populations have uniquely adapted to the rapid modernization of our environments,” Usui expressed.
For Francesco Cappello of the University of Palermo, Italy, this research underscores that even relatively young human populations are not fixed at a specific physical standard but continue to undergo modification. “This raises crucial inquiries regarding the interplay between genetics and environment, particularly concerning traits traditionally regarded as quite stable, such as skeletal biomorophology,” he remarked.
The study’s outcomes suggest that scientists may need to revise their established standards for identifying human remains, according to Kimberley Plomp from the University of the Philippines Diliman. “If the morphology of modern human skulls, and potentially other bones, has significantly altered over such a brief span, it implies that the methodologies we currently employ may not be as accurate as presumed,” she said. “This has profound implications for both biological and forensic anthropology.”
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